Asymmetric strain in nanoscale patterned strained-Si/strained-Ge/strained-Si heterostructures on insulator

The engineering of asymmetric strain is demonstrated in nanoscale patterned strained-Si/strained-Ge/strained-Si heterostructure on insulator with body thickness of 15 nm. Starting material has layers with symmetric in-plane strain, including biaxial strained Si (similar to 1.8%, tension) and biaxial strained Ge (similar to 1.8%, compression). Micro-Raman spectroscopy is utilized to characterize the stress in heterostructures patterned into 10-mu m-long bars with widths ranging from 300 to 30 nm. Raman measurements are consistent with the transformation from biaxial to uniaxial compressive strain in the Ge for 30-nm-wide bars, as predicated by simulations. Measurements also demonstrate enhanced asymmetric relaxation in the tensile strained Si cap as its thickness is increased. (C) 2007 American Institute of Physics.